Light-modulated dynamics in a novel mammalian circadian oscillator model

Circadian rhythms dictate our daily schedules in behaviour and physiology, and disruptions of normal circadian cycles therefore have potential to cause disorders of diverse physiological processes. A fundamental characteristic of circadian timing is the ability of the clockwork to be entrained by environmental time cues. In this paper, we mainly focus on the light-modulated dynamics in a novel model for the mammalian circadian clock which incorporates both the negative and positive feedback loops. It is shown that such a model not only can be entrained by light-dark (LD) cycles with equal distribution of night length and day length as observed experimentally, it can also be entrained by irregular LD cycles. The phase of circadian oscillations is significantly affected with the variation of LD cycles, demonstrating adaptation of the mammalian circadian clock to LD cycles. Finally, through numerical simulations and theoretical analysis we found a constructive role of light, i.e., the LD cycles can recover the circadian rhythmicity of gene knockout mice. These results might aid our understanding of the exploitation of light in the mammalian circadian rhythm generation.